Electric drive for die casting machines for plastic masses



Feb. 26, 1935. H GASTROW 1,992,696

ELECTRIC DRIVE FOR DIE CASTING MACHINES PLASTIC MASSES Filed Dec. 6, 1933 ,Ewezz' Patented Feb. 26, 1935 'PATENT OFFICE ELECTRIC DRIVE Foa DIE CASTING MACHINES roE PLASTIC MAssEs Hans Gastrow, Zerbst in Anhalt, Germany, al-

signor to Franz Braun Aktiengesellschaft,

Zerbst, Germany Application December 6, 1933, Serial No. 701,229 In Germany December 10, 1932 9 Claims. (Cl. 18-12) The present invention relates to an electrically driven die casting machine for casting plastic masses. Such machines usually comprise a pump having its cylinder connected to a illling hopper containing the material in powder form, each suction stroke of the pump piston causing a quantity of the material to pass from the hopper into the cylinder, to be then forced by said piston at high pressure into a heating cylinder l0 adjoining the pump cylinder, in which the material becomes liquid by the action of the heat and pressure. Towards the end of the pressure stroke the material is injected into the mold through a nozzle, the injection taking place if percussively. For this purpose a Valve is arranged in the nozzle and is kept closed until near the end of the pressure stroke. During and after the injection, the pressure on the pump piston must be maintained, not only to create the injection pressure, but also to keep the injected material under pressure whereby shrinking of the material in the mold is prevented. This pressure must be exerted, therefore, as long as any appreciable advance of the piston occurs, so

.25 that there is no definite terminal point of piston stroke.

The provision oi a reciprocatory drive having no ilxed stroke end and in which a very high pressure must be exerted at the stroke end, while the piston is stationary, amounting in some cases to 1000 atmospheres, to force the material in a ,I brief period through the ilne nozzle, can be achieved fairly easily by means of compressed air or liquid, but to effect such a drive by mechanical means, diiiiculties have to be overcome. The use of compressed air or liquid is not economical as it requires expensive compressor apparatus of low eiilciency.

An object of the present invention is to provide an electrical drive which in combination with simple mechanical auxiliary means will satisfy all the requirements of such die casting operations.

According to the invention an electric motor is used which has such characteristics, or can be so controlled by insertion o1' resistance in its armature circuit, that towards the end of the working stroke of the pump piston, the motor when brought to stoppage by the increasing re- 60 sistance of the material, will still exert its torque. Such a motor can drive the pump piston through a suitable transmission since a mechanical limiting of its working stroke is unnecessary. The motor can remain stalled for the interval in question and the reclprocatory motion may be obtained by electrical reversion of the direction of rotation of the motor.

The drive conditions oi the motor may be improved by inserting a spring between the drive and the pump piston, in such a manner that it is gradually tensioned while the resistance of the material to compression is increasing. The design of the spring is such as to effect a considerable storage of energy in this period which can be turned to account for the injection oi the material into the mold thereby relieving the motor to a corresponding extent.

The accompanying drawing schematically shows iii- Fig. l a longitudinal sectional view of the die casting machine,

Fig. 2 a sectional view on the line II--II of Fig. 1, and

Fig. 3 the diagram oi' connections.

In the drawing, 1 designates the funnel feeding the material to the die casting pump, and mounted on the cylinder 2 of a pump for compressing the powdered material, 3 being the piston of the pump. The numeral 4 signifies the electric heater of the die casting cylinder 4a, and 5 the nozzle to be opened or closed by a cock 6 which is, as diagrammatically shown, controlled by a lever 7 and rods 8. The mold into which the plastic material is injected is designated by 9. The pump piston 3 is driven by a piston rod 10 slidably mounted within a hollow spindle 11 which is externally threaded. This threaded spindle ll is guided in a housing 12 and secured against angu lar displacement e. g. by groove and tongue as at 12a. The threaded portion oi the said spindle 11 carries an internally threaded bush 13 which is a worm wheel externally and meshes with the worm 14 keyed on the shaft 15 of the motor A. The said bush 13 runs in ball bearings 13a in turn mounted in the housing 12. The shaft 15 of the motor is also provided with ball bearings 16 mounted in said housing 12. The free end of the piston rod 10 is threaded and, by means of a nut 17, fastened to one end of the bush 18 the other end oi which is provided with a flange 19. The spindle 11 is at l'20 screwed into one end of a spring 'casing 2l, in the other end 22 of which the spring bush 18 is slidably mounted. Between the said end 22 of the casing and the flange 19 of the spring bush 18 is an inclined stop 24 which in a deilnite position controls the reversal ol' the direction of rotation of the motor.

The device works as follows:-

By the motor A and the worm 14 the bush 13 is imparted a rotary movement which causes the nals v and mediary of threaded spindle 11 to move in the direction of the arrow (see Fig. 1),. The said spindle takes along the spring casing 21 together with the spring 23, which may be of the helical type. and compresses the flange 19 of the bush 18 which is thus entrained. The bush 18 moves the piston rod 10 to which it is fastened, and consequently also the pressure piston 3 in the direction of the arrow so that the powdered plastic material is pushed into the mass cylinder 4a against a very high counterpressure. Asduring this operation the said spring 23 is compressed a denite amount of power is accumulated which can be used for forcing into the mold material which has been liquefled in the cylinder.

The electric motor is e. g. of the asynchronous type and designed in the drawing by A. The amature winding of this asynchronous motor is continually short-circuited through an adjustable resistance b which is connected to 'the brushes of the slip rings and is intended for limiting the starting current and the current flowing when the motor is stopped under load. Adjustment of this resistance controls the maximum torque of the motor when stopped and thus the pressure acting on the piston. The terminals u, v, w of the stator winding are so connected to the triphase line U, V, W that the terminal w is directly connected to the wire concerned while the termiu are connected through the interan automatic change-over relay O which at the end of an adjustable time period reverses the rotation of the motor and can be mechanically actuated by the closure of the mold. This change-over relay connects the terminals v and u either tothe network terminals V and U respectively or inversely to the terminals U and V respectively. The time interval between two reversals as adjusted on the said change-over relay O is decisive for the stopping time inthe advanced position of the piston and depends on the work to be accomplished, viz. the properties of the material to be worked.

In the shown position ofthe relay the terminals v and u are directly connected to the wires V and U respectively by the change-over relay O. With this position of the relay the motor runs in a direction which causes the piston the direction of the arrow. After the said relay having changed its position for the opposite direction of rotation,` the terminals v and u are connected to the contacts v' and u of the changeover relay Othrough the intermediary of a switch N. This switch N is intended for limiting the return stroke of the piston 3 and for cutting out the motor. To this end the spring casing 21 is provided with a stop 24 already referred to which in the right-hand position of the spindle 1l opens the switch N by means of its inclined surface and so cuts out the contacts and terminals u and v'.

Instead of an asychronous motor also other types of motors may be used provided that they comply with the requirement that in case oi' an increase of the resistance opposed to the operation performed by the motor, the speed of the motor can decrease to stoppage while the torque thereof is maintained. l

What I claim as my invention, and desire to secure by Letters Patent, is:-

1. In an electric drive for die casting machines for plasticmasses, a mechanism for forcing the casting mass into a mold, an electric motor for driving said mechanism, and means for main- A 3tomovein` 'casting mass into a :,coaene taining the motor torque operative on said mechanism after stoppage of the motor by its load.

2. In an electric drive for die casting machines page by its load.

3. In an electric drive for die casting machines for plastic masses a mechanism for forcing the casting mass into a mold, an electric motor for driving said mechanism, an adjustable resistance in the armature circuit of said motor, and automatic means for adjusting said resistance during operation to allow maintenance of the motor torque after stoppage of the motor by its load.

4. In an electric drive for die casting machines for plastic masses, a mechanism for forcing the casting mass into a mold, an electric motor for driving said mechanism, an adjustable resistance in the armature of said motor, and automatic means for adjusting said resistance, said motor having such characteristics that in cooperation with the said resistance its torque may be maintained after stoppage by its load.

5. In an electric drive for die casting machines for plastic masses a mechanism for forcing the casting Inass into a mold, an electric motor for driving said mechanism, means for maintaining the motor torque after stoppage of the motor by its load, and a switch with timing control for reversing the motor after the lapse of a predetermined time.

6. In an electric drive for die casting machines for plastic masses a pump mechanism with a piston for forcing the casting mass into a mold, a reversible electric motor for driving said machine, means for maintaining the motor torque after stoppage of the motor by its load, and contact means controlled by the pump piston for switching otl' the motor upon return of said piston to original position.

7. In an electric drive for die casting machines for plastic massesa mechanism for forcing the casting mass into a mold, an electric motor for driving said mechanism, a mechanical transmission gear between the said motor and the said mechanism, a spring adapted to accumulate power between the transmission and the pump piston, and means for maintaining the motor torque operative on said mechanism after stoppage of the motor by its load.

8. In an electric drive for die casting machines for plastic masses a mechanism for forcing the mold, an electric motor for driving said mechanism, a self-locking mechanical transmission between the said motor and the said mechanism, a spring adapted to accumulate power between the transmission and the pump piston, and means for maintaining the motor torque operative on said mechanism after stoppage of the motor by its load.

9. In an electric drive for die casting machines for plastic masses a mechanism for forcing the casting mass into a mold, an electric motor for driving said mechanism, adjustable resistances associated with the armature circuit of said motor, and current controlled relays for switching an increasing number of said resistances into the said armature circuit when a predetermined amperage has been reached in the motor circuit.

HANS GASTROW. 

